1. Field of the Invention
The present invention relates to systems for driving the transducers in ink jet print heads. In particular, to a drive system with a voltage source having waveshape circuit for shaping the voltage supplied to the transducers and a method of operating the source.
2. Description of Related Art
In typical ink jet printers, a print head having one or more ink jets is moved back and forth over a target. As the print head moves, ink drops are ejected from the ink jets and impact the target to form images. The printer is generally provided with a controller which monitors movement of the print head and controls ejection of the ink drops such that the drops hit the target in the proper locations to form desired images.
Each ink jet in such print heads typically includes a orifice in communication with a variable volume chamber. The chamber is filled with ink supplied from an ink reservoir. A transducer is coupled with the chamber such that activation of the transducer causes the volume of the chamber to change to thereby eject a drop of ink from the orifice toward the target. A voltage source, typically not located on the print head, supplies a constant voltage to the print head. A drive circuit on the print head, in response to signals received from the controller, activates any particular transducer by coupling it to the constant voltage source at the desired time.
It is known that the shape and velocity of the ejected ink drop, and other factors which influence the ultimate quality and resolution of the printed image, depend, to some extent, on the excitation waveshape the plot of voltage applied to the transducer over time, applied to the transducer. Therefore, it is usually desirable for each transducer to be driven with the same excitation waveshape. It is also frequently desirable to drive the transducers with a particular waveshape to achieve ink drops with desired properties. However, because of manufacturing variations and the like, each transducer typically has a slightly different capacitance. As a result, when the constant voltage is applied to different transducers, each having a different capacitance, the excitation waveshape for each transducer may vary slightly.
To compensate for this problem, each transducer in a print head is typically coupled with a series network, usually a series resistor to control rise time and a diode in series with a second resistor to control fall time, to adjust the individual excitation waveshape for each transducer to a desired excitation waveshape. However, as can be appreciated, the individual adjustment of the excitation waveshape for each transducer in a print head can be very inefficient and costly. More importantly, the provision of a series network for each transducer can consume a relatively large amount of space on a print head, particularly for print heads having a large number of ink jets. This frequently requires the use of larger, more cumbersome print heads, which can adversely affect many other aspects of printer performance and design.